When a cow is in the chute for pregnancy checking, many cow-calf producers take advantage of the opportunity to perform other necessary procedures to get their cows ready for the winter and the subsequent calving season. For some producers, vaccinating cows is on this list of tasks. But should it be?

There are two main disease categories for which most producers vaccinate cows. One of them is to boost colostrum quality by vaccinating against calf scours organisms. The other is for infectious reproductive pathogens such as IBR, BVDV, leptospirosis and vibriosis.

Most vaccines against reproductive pathogens are labeled to be given prior to breeding. In some herds, however, management and labor constraints result in situations where preg-check time is the only chance to get the cows vaccinated.

While it may be convenient, vaccinating for reproductive diseases during gestation is not exactly ideal. Most of the reproductive diseases we can vaccinate for can have substantial effects early (first two months or earlier) in gestation. Vaccinating a spring-calving cow herd in November means that 7-8 months might elapse between vaccination and the beginning of the next breeding season. This is long enough for the vaccine’s effects to have waned, as peak immunity probably occurs within a couple weeks of vaccination and then slowly declines. For this reason, gestational reproductive vaccine programs lack optimal timing.

It should be pointed out that there is little downside to using reproductive vaccines during pregnancy, if—and this is a big “if”—killed vaccines are used. Vaccinating the herd during gestation with a killed reproductive vaccine will probably provide the herd a better level of protection than not vaccinating at all.

In recent years, several vaccine manufacturers have promoted using modified live vaccines (MLV) in pregnant cow vaccination programs. It has long been known that administering modified live IBR vaccines to pregnant cows will result in abortions. This latest recommendation is therefore given with the caveat that animals must have been properly vaccinated pre-breeding that year with the same MLV vaccine.

However, evidence is mounting that this practice is a bad idea. Stories of devastating abortion storms following pregnant cow MLV vaccination exist. These initially were noted to occur as a result of producers not following the label precautions regarding properly vaccinating cows with the same product before breeding the first year. But in recent years reports of abortion storms in cattle herds using MLV vaccines according to the label directions have surfaced (O’Toole, et al), making even label use of these vaccines suspect.

Cattle producers know how difficult it is to maintain good reproductive rates in a cow herd when everything goes right. Given current information, it seems that the risk of using MLV vaccines in pregnant cows is not anywhere near the benefits that may be gained. Producers with questions about their vaccine program should consult with their veterinarian.